Controlling weeds in organic cucurbits requires the use of many
techniques and strategies in order to achieve economically acceptable weed
control and yields. Weeds can always be pulled or cut out, but the question is
simply how much can a grower spend in terms of time and money to reduce weed
pressure. The more a grower is able to reduce weed pressure (seed and perennial
propagules), the more economical it is to produce crops.

Monitor the fields and keep records of the weed species that occur
in each field during the period of the year when the crop will be grown,
especially at planting time but before hand weeding or cultivation to determine
what weeds have escaped treatment. Not only are these records valuable in
planning weed management strategies, but they also help track the occurrence of
hard-to-control weeds. At harvest, keep records of specific locations in the
field where weeds are producing seed. Weed patches are relatively stable within
a field and management of these weed clusters may improve weed control in
future crops. Avoid fields that have high populations of certain weeds such as
common purslane, field bindweed, or nutsedge, as these weeds are not adequately
controlled by currently available weed management methods.

Water
management
Water management is a key tool for controlling
weeds in cucurbits. There are a number of ways that careful use of irrigation
management can assist growers in reducing weed pressure. A process called
"pregermination" involves irrigating (or rainfall) before planting to
germinate weed seeds, which can then be killed by light cultivation or flaming.
Pregermination should be done as close as possible to the date of planting to
assure that the weed spectrum does not change with the changes in the season or
weather.

Dust mulches are also used in cucurbits. This technique is
compatible with the process of pregermination. After weeds are killed by
cultivation, the top 2 to 3 inches of soil are allowed to dry and form a dust mulch. At planting the dust mulch is pushed away and
large seeded cucurbits can be planted into the zone of soil moisture. The
cucurbit seed can germinate and grow with no supplemental irrigations that
would otherwise germinate another flush of weeds.

Drip tape buried below the surface of the bed can provide
moisture to the crop and minimize the amount of moisture that is available to
weeds on the surface. If properly managed, this technique can provide
significant weed control during the non-rainy periods of the year.

Cultivation
Cultivation is probably the most
widely used method of weed control in organic vegetable systems. Mechanical
cultivation uproots or buries weeds. Weed burial works best on small weeds,
while larger weeds are better controlled by destroying the root-shoot
connection or by slicing, cutting, or turning the soil to separate the root
system from contact with the soil. Cultivation is effective against almost all
weeds. Effective cultivation requires good land preparation for precision and
accuracy. Shallow cultivation usually is best, because it brings fewer weed
seeds to the surface. Level beds allow greater precision in depth of tillage.
Cultivation requires relatively dry soil conditions; delay subsequent
irrigations long enough to prevent re-rooting of weeds.

The goal of cultivation is to remove the weeds as close to the
seed row as possible without disturbing the crop. In most cases precision
cultivation can take care of weeds on over 90 percent of the bed. The remaining
weeds must be removed from the seed row by hand or other mechanical means.
Cultivation implements are often mounted on sleds for accurate, close
cultivation in row crops. Guide wheels, cone wheels, and other devices are also
used, but are generally less precise than sleds. Various implements are
attached to these guidance setups to remove weeds.

Even the best cultivators will not eliminate all weeds, thus hand
weeding is often needed. It is easier to remove weeds while they are small. The
proper timing between cultivations depends on the speed of weed growth: in
spring a 2- to 3-week period is about right, in the fall or winter, longer
periods between cultivations may suffice.

Early occurrence of persistent weeds may be more damaging to crop
yield than are weeds that establish late. Late-season weeding often disturbs
crop root system or knocks off flowers or fruit and consistently results in reduced
yields. Obviously, late season cultivations to reduce weed seed production must
be weighed against the potential for yield loss.

Flamers
Flamers can be used for weed control
with propane-fueled models being most common. Fire causes the cell sap of
plants to expand, rupturing the cell walls. Flaming can be used before the crop
emerges. Weeds must have less than two true leaves for greatest efficiency of
the burner. Grasses are harder to kill by flaming because the growing point is
below the ground. After flaming, weeds that have been killed change from a
glossy to a matte finish. This occurs very rapidly in most cases. Typically,
flaming can be done at 3 to 5 mph through fields, although this depends on the
heat output of the unit being used. Best results are obtained under windless
conditions, as winds can prevent the heat from reaching the target. Early
morning or evening are the best times to observe the
flame for adjustment.

Mulches
Mulches blocks
light, preventing weed germination or growth. Many materials can be used
as mulches including plastics or organic materials such as municipal yard
waste, wood chips, straw, hay, sawdust, and newspaper. To be effective, a mulch needs to block all light to the weeds therefore
different mulch materials vary in the depth necessary to accomplish this.

Plastic mulches vary in thickness from 1.5 mil to about 4 mil. The most common plastic color for weed control is black, as it
completely blocks light. Plastic mulches are generally placed on the beds and
their edges covered with dirt to prevent their blowing away. Drip irrigation is
needed under the plastic mulches to provide the crop with moisture. Certain
weeds such as nutsedge are not completely controlled by plastic mulches,
because they are able to penetrate the plastic. Other weeds are also able to
grow in the openings provided for crops. Further problems with plastic mulches
include maintaining them in place under windy conditions, disposal after crop
harvest, and the cost (including the need for drip irrigation).

Organic mulches such as municipal yard waste, straw, hay, wood
chips, etc., must be maintained in a layer 4 or more inches thick. Coarse green
waste works better as a mulch. Organic mulches can also be grown in place.
Plants used in this way include subterranean clovers, ryegrass, fava beans,
oats, barley, rye, etc. These mulches (or living mulches as they are sometimes
referred) must die or be killed before planting the crop to avoid excessive competition
with the crop.

Organic
herbicides
Herbicides are chemicals that kill or
suppress plants by affecting plant physiological processes. The number of herbicides that are organically acceptable are
limited and include contact materials such as citric acid, clove oil, cinnamon
oil, lemongrass oil, and various soaps. Herbicides can be used to selectively
control weeds by application ahead of crop emergence or by use of shielded or
directed applications. These herbicides kill plants that have emerged, but have
no residual activity on those subsequently emerging.

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